Studies On Baking And Nutritional Properties Of Kluyveromyces Marxianus Fermented Wheat Bran Bread

In this study,Kluyveromyces marxianus with ?-glucosidase producing ability was used to ferment wheat bran(WB)as functional ingredient with natural enzymes,and biochemical components of WB were analyzed during the fermentation process.The fermented WB(FWB)was used in high dietary-fiber bread making,and its impact on baking properties and nutritional characteristics of bread was studied.The different breads produced for analysis were: bran dough and bread(BD/BB),fermented bran dough and bread(FBD/FBB),xylanase bran dough and bread(XBD/XBB)and xylanase fermented bran dough and bread(FXBD/FXBB).The main results of the study are:K.marxianus exhibited extracellular ?-glucosidase production ability,and the activity in supernatant reached a value of 6.98 U/g.The ?-glucosidase activity of yeast mud showed no intracellular type,but 96% of it was located in ultrasound precipitation.Fermentation parameters were optimized using single factor and response-surface optimization methods: inoculation volume 6.0%(v/w),dough yield(DY value)190,and fermentation temperature 30?.Study on biochemical properties of femented WB during fermentation process showed that K.marxianus grew well in fermented WB.The TTA value increased from 7.8 to 18.7 mL,but the pH decreased slightly by 7.81%.During the fermentation process,endoglucanase and xylanase activities showed an initial increase,followed by a decline,with the highest activities at 6h(respectively 2.93 and 0.35 U/g);exoglucanase and ?-glucosidase activities continued to increase,and reached final values of 6.06 and 21.70 U/g respectively;ferulate esterases showed the highest activities at 36 h(0.16 U/g).During the fermentation process,insoluble dietary fiber(IDF)and water-unextractable arabinoxylan(WUAX)degraded continuously,with the highest concentration of soluble dietary fiber(SDF)and water-extractable arabinoxylan(WEAX)at 24 h.Also,during fermentation process,WB released phenols and ferulic acid;reducing sugars accumulated at the initial 6 h with a concentration of 15.2%(w/w);ethanol increased dramatically at 6 h,and remained steady after 30 h.K.marxianus fermented WB with natural enzymes improved baking property of bran enriched bread.Compared to BD,water absorption of FBD,XBD and FXBD decreased by 5.64%,6.94% and 6.45% respectively.Dough development and stability time of XBD decreased,but an opposite trend was observed in FBD and FXBD.Compared to BD and XBD,FBD and FXBD had a higher development height,higher gas-hold rate and lower gluten weakness.Scanning electron microscope(SEM)showed that the gluten network structure in dough with fermented bran was continuous and well-distributed,and characterized by few and irregular small pores.Compared to BB and XBB,FBB and FXBB showed higher specific volume,lower firmness and higher water-hold capability.During bread making,free phenol and WEAX content increased continuously,especially in FBD and FXBD enriched with many natural enzymes.After mixing,BD showed the highest molecular weight.After fermentation,WEAX molecular weight further decreased in the order: BD>XBD>FBD>FXBD.After baking,FBD had a similar molecular weight to FXBD,but much higher than XBD.Study on solubility of dietary fiber and arabinoxylan showed that no visible differences in DF content of four breads was observed,and the SDF content of FBB and FXBB were 4.12 and 4.37 g/100,respectively.Similarly,the WEAX content of FBB and FXBB was higher in BB and XBB.Fermented bran enriched bread showed higher degree of branching for WEAX compared to bread with raw bran,an opposite trend observed with AX.BB had phytic acid content of 8.40 mg/g,which decreased by 8.97%,45.54% and 49.94% in XBB,FBB and FXBB,respectively.Simulated gastrointestinal digestion showed that free phenol content in wheat bread(WFB)was 0.58 mg/g;which was lower(p<0.05)than that of BB and XBB,while FBB and FXBB had a content of 1.82 and 1.91 mg/g.After gastric digestion simulation,the free phenol content of WFB,BB,FBB,XBB and FXBB increased by 4.12,1.90,2.13,2.34 and 2.31 times,respectively.After intestinal digestion simulation,the free phenol content varied from 2.34 to 5.06 mg/g,and phenol absorption in FXBB was highest at 0.99 mg/g.After gastrointestinal digestion simulation,ferulic acid was released,of which 67.80%~72.30% was absorbed.FBB and FXBB had the highest absorption rate compared to others.